Fig. 4

a Scan over the strength of an additional electron sink to identify the amount of additional reduction required to predict the experimentally observed by-product formation. Predicted ratio of ethanol/butanediol shifts towards 2,3-butanediol in response to oxidized medium. Positive values indicate additional flux through the DEHOG reaction and thus either an increased demand of reductant or a more reduced biomass. Markers show the experimental values for biomass, ethanol and 2,3-butanediol production. The simulated outputs fit well to these when using FHL and an adjusted redox demand of +0.7/biomass carbon (see text). b Scan over a range of maintenance ATP required per biomass carbon as in Fig. 3, but with FHL and an additional reductant requirement of +0.7/biomass carbon, as determined by Fig. 4a)